Commuters queue to get on to the Luas Red Line at Heuston Station this morning. Photograph: Damien Cullen/The Irish Times

A trade union has warned legal proceedings being brought by Dublin Bus and Bus Éireann over the 48-hour bus strike which started on Friday morning will only harden of the resolve of striking workers.

The companies are to lodge papers in the High Court on Friday as part of a claim against Siptu and the National Bus and Rail Union (NBRU) to recover millions of euro in lost revenue and fines that will be imposed on foot of the disruption to services.

No Dublin Bus and Bus Éireann services have been in operation since midnight in a dispute over plans by the National Transport Authority to put out to tender 10 per cent of routes currently operated by the State-owned companies.

Hundreds of thousands of people have had their travel plans disrupted as a result of the strike.

Traffic was disrupted for a short while in Dublin city centre when striking workers marched behind union banners down O’Connell Street this morning. .

Tanaiste Joan Burton urged all those involved to sit down and try to negotiate.

“I hope all parties will sit down and negotiate the only way to resolve a dispute like this is to sit down and have negotiations, and I hope it will possible to do that as quickly as possible”

A Bus Éireann spokeswoman said that it had gone to court as a last resort.

The transport companies say the strike is illegal, a charge rejected by trade unions.

In a letter issued Friday, the general secretary of the NBRU Dermot O’Leary criticised management in both companies as well as in the National Transport Authority.

He said a recent intervention by the chief executive of the Authority Anne Graham had “led to a crystallisation of the fears and concerns of members”.

Mr O’Leary said the legal action being initiated by the chief executives of the two State transport companies had “done a disservice to your employees and our customers, attacking workers and their representatives”.

He said this could but lead to a hardening of staff resolve.

“The NBRU remains implacably opposed to privatisation. We will continue to highlight this flawed ideologically-based attempt to hijack publicly-owned bus companies. We will continue to highlight the fact that this policy is a bad deal for the taxpayer and we will continue to focus on our contention that this is a race to the bottom.”

Employers’ group Ibec said the industrial action would cause massive and unnecessary disruption to the travelling public and businesses alike. It urged all parties to the dispute to resume talks with a view to resolving the issue.

“Minister for Transport, Tourism and Sport Paschal Donohoe has addressed the workers industrial relations concerns regarding the potential transfer of employees to operators in the private sector. The remaining issues are questions of public policy and as such are not appropriately advanced under the protections of the Industrial Relations Act, 1990.”

Speaking at the Dublin bus depot in Summerhill, NBRU representative Brendan Hayden said he and his colleagues were protesting over the plans to put routes out to tender.

“It is off-the-wall that they are proceeding with this. There is no need for privatisation. Unfortunately while we were invited to the LRC, the NTA/Government had nothing to offer. We are just looking for the protection of our pay and conditions in 2019 and not just now.”

Dublin Bus says it will lose revenue of €600,000 per day as a result of the strike while Bus Éireann expects to lose revenues of €1.5 million.

Talks to avert the strike broke down last night after 2 1/2 hours of discussion at the Labour Relations Commission (LRC) with both sides blaming the other for the impasse.

The bus companies expect that up to 1.1 million bus journeys will face disruption over the 48-hour period. Dublin Bus said it normally carries 450,000 customers on a Friday and 400,000 customers on Saturday while Bus Éireann said the strike would result in the loss of an estimated 250,000 passenger journeys.

Drivers at Dublin Bus and Bus Éireann voted overwhelmingly in April to back strike action in protest. NBRU members in Dublin Bus voted by 92 per cent while those in Bus Éireann voted by 91 per cent in favour of industrial action.

Gardaí said they and local authorities will continue to monitor the situation but “at this stage there is no plan to open the bus lanes up to other motorists.”

Gardaí are advising motorists to allow extra time when planning their journey during the strike.

Mr Donohoe said the strike action was “unjustified and will cause considerable damage to an economy that is in recovery, have financial implications for the bus companies who are only just getting back on their feet and discommode the travelling public who are attempting to go about their daily business”.